Cytogenetic, Serologic, and Transplantation Studies on a Heterozygous Tumor and Its Derived Variant Sublines

Abstract

The MSWB sarcoma has been induced by methylcholanthrene in an (A♂ × A. SW♀)F₁ hybrid mouse (genotype H-2^a H-2^s). When tested in both parental strains, the sarcoma gave rise to 24 percent progressively growing tumors in the A.SW maternal strain. No tumors were ever obtained in the paternal A strain. When tested in A.SW mice preimmunized against tissue of strain A origin, the yield of tumors obtained after the inoculation of the original line decreased to 2 percent. On the other hand, the tumors that have developed in the A.SW mice, referred to as variants, showed a very high ability to grow in A.SW mice upon subsequent testing (92% on the average) and also in preimmunized mice (86%). Serologic analysis has demonstrated that the original line of MSWB contains the following H-2-determined isoantigenic components: D and K (derived from strain A), SG (derived from A.SW), and E and F (common to A and A.SW). Nine variants studied did not contain D and K in detectable amounts, while S, G, E, and F were still present. This was in agreement with the transplantation tests. One exceptional variant selected in an (A.SW × DBA/2)F₁ hybrid has probably lost K only, as indicated by transplantation tests. Experiments involving the inoculation of very small cell numbers and studies on the detailed chromosome cytology of the original tumor and 10 different variants indicated that the repeated detection of variants in A.SW mice was mostly due to independent events. With the exception of 2 variants, derived from the same original inoculum pool and showing closely identical karyotypes, all of the others were different from each other and from the original tumor with regard to their detailed chromosome cytology.